Efforts to reduce a dry cleaning chemical in town water appear to be working. The announcement was made at an Arizona Department of Environmental Quality (ADEQ) meeting to update residents on the cleanup of Payson's contaminated groundwater Tuesday night.
In 1990, high levels of a common dry cleaning chemical, tetrachlorethylene or PCE, was found in town wells. The town water department and the ADEQ took action and, by 1993, declared the source area a Water Quality Assurance Revolving Fund Site (WQARF) -- the state's version of a national superfund site.
The environmental cleanup of the solvent, which has been determined to be a human carcinogen, has consisted of:
- An elaborate water treatment facility;
- Cleanup of soils through soil vapor extraction to inhibit further contamination and exposure;
- Extensive testing to map the plume of contaminants and contain the spread of the pollutant.
In the meantime, a second site was found around the now-defunct Grandway Cleaners in Bonanza Square. This area became known as the Tonto & Cherry WQARF site.
Project hydrologist David Haag summarized recent findings at the original Payson PCE site.
"We collected our last round of sampling in March and our findings were consistent with previous data," Haag said.
"The monitoring wells east of McLane Road and near the plume had PCE concentrations of 5 parts per billion (ppb)."
Haag also said that samples from monitoring wells around Rumsey Park did not show PCE, except for the rodeo grounds well, which came in at 6 ppb.
The findings mean that the remediation was successful in reducing the pollutant to safe levels according to both state and federal standards.
Early testing, prior to installation of the treatment facility that has large carbon filters, revealed levels of 20,000 ppb of PCE in town wells.
"The concentrations were lower than expected, but there are still a few hot spots," Haag said. "The monitoring well behind the Texaco came in at 75 ppb."
By turning on one of the town wells, Haag explained, they were able to draw the contaminated water from the hot spots toward the treatment plant.
A feasibility study suggesting other cleanup options has been in the works for the last several months and is in its final stages of review. Normally, the study is done prior to cleanup, but ADEQ chose to take what is called an early response action due to Payson's unique and limited water supply.
"The feasibility study is being reviewed by management," Haag said. "We still don't know when it will be completed."
Once the study is completed, there will be a series of hearings in which the public can comment on the document.
The Payson PCE WQARF site has, so far, cost the state between $8 to $9 million.
"We have removed 550 pounds of PCE from the site, which is about two barrels," Haag said. "It doesn't take much to contaminate an aquifer."
The Tonto and Cherry WQARF site is still in the remedial investigation stage and the town and ADEQ are taking samples from monitoring wells in the Bonanza Square area.
"The March sampling came back with a reading of 5.4 ppb of PCE," Haag said. "Just slightly above the state and federal standard of 5 ppb."
Haag also reported a new finding below the old Grandway Cleaners. "We found Trichlorethylene, TCE, at a level of 8 ppb," he said.
Residents in the immediate area, including an adjacent trailer park, have been supplied with bottled water because they were getting water from a nearby well rather than from the town.
"The trailer park has now been hooked up to city water," Haag said, "so we are no longer supplying those residents with bottled water."
No cleanup has been done at the Tonto and Cherry site for two reasons, according to Haag. "The highest levels of PCE we found were 54 ppb and the latest readings are close to the standards," he said.
"We put in pumps, but were getting only one to two gallons per minute," Haag said. "It was too little water to treat."
Haag said that the low concentrations may warrant no further action than continued monitoring.
During the prior meeting in February, it was announced that the gas additive Methyl Tertiary Butyl Ether (MTBE) was found in low levels in water that had been treated, indicating that the treatment method was not completely effective in filtering out MTBE.
Although a major study at the University of California in Davis found that MTBE is harmful to humans, and some states have banned its use, the Environmental Protection Agency has not assigned a "safe" standard to the chemical, which was initially added to gas to make it burn more completely, thus improving air quality.
Before gas stations were required by federal law to have dual-sided storage tanks, leakages frequently occurred, making groundwater vulnerable to contamination.
What was unknown at the time, was that MTBE, unlike solvents, moves very quickly through water and does not bind to filters easily, making remediation difficult.
The monitoring that resulted from the PCE contamination, alerted town and state officials to the presence of the MTBE.
"We still have some MTBE coming out," Haag said. "I think around .8 ppb."
Although there is no national standard for MTBE, a health-based guidance level for children is 94 ppb and the taste and odor threshold is 35 ppb. MTBE, at higher levels, has a strong gasoline-like odor.
The feasibility study may suggest some methods to eliminate MTBE if detectable levels continue seep through the filtration process.
The next meeting to update residents on the WQARF sites is scheduled for Sept. 9. To receive notification about the meeting or for more information, contact ADEQ community involvement coordinator Tina Wesoloskie at (800) 234-5677.